Cryogenic electrical transformer apparatus having double wall construction

ABSTRACT

To prevent excessive deformation upon short circuit or other stresses tending to push spaced walls together, while avoiding heat loss by conduction, spacer members having teeth facing an opposed wall are applied to one wall, some of the teeth being recessed by 0.1 to 1 mm from the facing wall so that contact obtains only upon deformation. A suitable material for spacers is epoxy bonded fiber glass.

United States Patent Vayson de Pradenne s41 CRYOGENIC. ELECTRtQAL TRANSFORMER APPARATUS HAVING DOUBLE WALL CONSTRUCTION lnventor:

Assignee:

Filed:

Appl. No;

France References Cited UNITED STATES PATENTS Henri Vayson de Pradenne, Paris,

Alsthom-Snvoisienne, Ouen, France Sept. 4, 1969 US. Cl ..220/15, 138/113 Int. Cl. ..B65d 25/00 FieldofSeurch ..220I15,10,'9 LG; 138/113,

12/1919 Hettinger; ..'.220/ 15 X 2/1920 Allison ..220/15 X Mott et a1 .'.....220/10 Zenner ..220/15 [451 Sept. 19, 1972 2,065,006 12/1936 Zivanov ..220/15 2,076,550 4/1937 Conner ..220/10 UX 2,763,321 9/1956 Schuster ..220/15 X 3,045,858 7/1962 Sohngen ..220/15 X FOREIGN PATENTS OR APPLICATIONS 462,059 12/1949 Canada 138/1 13 Primary Examiner-Joseph R. Leclair Assistant Examiner-James R. Garrett Attomey-Flynn & Frishauf 11 ABSTRACT 12 Claims, 5 Drawing Figures COGOGENIC'ELECTRICAL TRANSFORMER I I APPARATUS HAVING DOUBLE WALL CONSTRUCTION The present invention relates to spacing arrangements for walls to be used in installations functioning at very low temperatures, at less than 200C for example, and more particularly to walls enclosing electrical devices in a compartment retaining cryogenic fluid which must be thermally isolated by means of airtight enclosures subjected to extremes of vacuum.

' In a cryotransformer, which must function at the temperature of liquid hydrogen, an assembly of concentric airtight enclosures is so located as to surround an inner compartment intended to contain the transformer submerged in a cryogenic medium; these enclosures increase the thermal isolation when under extreme vacuum, maintaining the cold within the inner compartment and protecting against thermal seepage.

If .a short circuit occurs in a cryotransformer or, generally, any over-pressure of cryogenic fluid occurs in an installation functioning at extremely low temperature, the walls of the thermal isolation enclosures can be subjected tov extreme stresses that they could be incapable of sustaining by themselves. The introduction of reinforcement elements within these enclosures conflicts with the necessity of avoiding bridging members of mediocre thermal isolation properties between the two walls of the enclosure, and particularly excessively thick ones for mechanical strength.

It is an object of the present invention to provide a spacing arrangement placed between two walls of an enclosure serving to thermally isolate from one another two media at very different temperatures of which one is lower than 200C.

SUBJECT MATTER OF THE PRESENT INVENTION Spacers are provided between the walls which have at least in the direction toward one of the walls a toothshaped portion which, in the case of an incident tending to force these walls together, obviates all risk of deformation and at the same time minimizes thermal exchanges from one wall to the other. To this end at least a part of the said teeth are arranged to come into contact with the wall only in the caseof an incident tending to force the said walls together.

It is advantageous to give the teeth a trapezoidal shape so as to avoid concentration of stresses on projecting points.

Thermal leaks by radiation from the wall are reduced by metalizing the support surfaces of the teeth which come into contact with the wall only occasionally.

The best material to use for the spacer elements is a composition made up fabric or glass fiber plies bonded together by a synthetic resin, preferably an epoxy resin.

Contrary to every expectation, the best results were obtained using a layered material bonded under high pressure whose fabric orglass fiber plies ran parallel to the stress to be sustained, and in which the teeth were machine-stamped.

The space left in the normal state between wall and teeth coming only occasionally into contact with it may be between approximately 0.1 mm and 1 mm.

The spacers are best held in place by means of the teeth that are in permanent contact with the wall, since these present a support surface of much less area than the occasional support surface. More specifically, the area of this permanent support surface may be in the order of one-tenth of the area of the occasional support surface and, with an epoxy glass fiber material, one one-thousandth of the surface of the corresponding wall.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 represents an axial section of the thermal isolation enclosure of the compartment containing the windings of a cryotransforrner with but a single spacer plate 12 being shown in the interest of clarity.

FIG. 2 exhibits, on another scale, a horizontal section of a portion of this enclosure with spacer element,

' taken in the plane 2-2 of FIG. 1.

FIG. 3 shows a tooth of a spacer element.

FIGS. 4 and 5 show, in section the mounting of spacer elements. Y

The thermal isolation enclosures preferably employ a layered material, for example, one having a base of glass fiber and epoxy resin or polyester. Such material is an electric insulator and is suitable mechanically,

since it maintains its strength at extremely low temperatures, is resistant to thermal shocks undergone while being placed in such temperature, and is impermeable to cryogenic gases. Furthermore, this material is relatively light and permits ready manufacture of tanks or enclosures by assembly of cylinders, made by known technique of medium pressure rolling, with disks, machined from the same material in a plane shape. The disks permit concentric mounting of the cylinder so that closed annular containers with cylindrical walls and flat bottoms result.

A cylinder 1 (FIG. 1) forms the inner extreme wall of the thermal isolation enclosure; the central magnetic core 2 of the cryotransformer, is only schematically shown.

Walls 3 of the cylinder define a compartment 4 filled with cryogenic fluid. The space lift between walls 3 and cylinder 1 is under vacuum and forms part of a thermal isolation enclosure.

A cylinder 6 forms the other wall of cryogenic compartment 4, cylinders 3 and 6 being joined by solid ends 7 and 8. Scalable openings, not shown, are formed therein to provide terminals, the circulation for ducts for cryogenic liquid, etc.

A cylinder 9 form an outer wall facing the outside of the thermal isolation enclosure 5, the space left between cylinders 6 and 9 being part of the thermal isolation enclosure 5, is closed by solid heads 10 and 11 joining cylinders l and 9 and completely surrounding compartment 4.

In the case of cryotransformers of great power, of the order of 15 to 20 MVA, difliculty is encountered by the instantaneous electrodynamic stress which the structure must sustain whenever the transformer is thrown into short circuit. Short circuits result in over-pressure of cryogenic gas, for example hydrogen, whose pressure in the order of l kg/cm in normal service, may surpass roughly 5 kg/cm, exerted in all directions.

As is known, short circuits are accompanied by a mechanical stress directed along vectors of force oriented toward the central magnetic core, and tending to result in an implosion affecting the low tension coil.

In order to anticipate any displacement of the low voltage coil within cryogenic enclosure 4, the mounting of the coil of the cryotransformer is effected, as known by means of holding strips parallel to the axis of the walls, and placed during the winding of the coil conductor; these strips prevent any deformation of the structure from a possible short circuit while permitting the free circulation of cryogenic liquid around the coils. The mechanical stress is then transmitted to cylinder 1; as is known, stress is not necessarily uniformly distributed,

but may exhibit asymmetrical components due to excentricities in the coil, so that concentrations of local stresses may result. For a cryotransformer of to KVA placed in an annular enclosure in which the surface of cylindrical wall 1 is 30,000 cm, the instantaneous overall implosion stress resulting from a short circ'uit would be roughlyl,000 tons, or 33 kg/cm, if it were-evenly distributed over the surface of this wall.

"So as to sustain such shock stresses,'it has been the practice to mechanically reinforce the inner wall of a transformer by means of outside supports. In the case of a cryotransformer placing a mechanical reinforcement, for example, ribs supported against the wall of cylinder 1, conflicts with the requirement that annular compartment 5, in which it would be lodged, forms a thermal isolation enclosure between the low temperatures with which the cylindrical wall 3 is in contact and the ambient temperature which is that of cylindrical wall 1, so that any element connecting these two cylindrical walls would constitute a bridge for thermal leakage interfering with efficient operation of the cryotransformer.

In accordance with the invention, spacers formed of an assembly of toothed rings of a laminated material are" provided. Rings 12 (FIG. 2) impregnated with an epoxy resin, rest with a solid part against cylindrical although, as will appear below, the strength of such a construction is less.

In order to determine the minimal total surface of support points needed to maintenance of spacing at the moment of maximal short circuit stress within the cryotransformer and to preclude-the possibility of any excessive deformation of the device, it is advisable to choose this total support surface in such a manner that the stress sustained by the reinforcement elements does not exceed their mechanical resistance to compression.

With laminated materials of glass fiber and epoxy resin it was found that a total surface of contact points representing I percent of the lateral surface of cylindrical wall 1 is mechanically acceptable given the resistance of the material, if certain precautions, which willbe specified below, are taken.

It was found possible to reduce by nine-tenths the above-mentioned permanent support surface and to reduce in the same proportion permanent undesirable thermal leaks by utilizing a spacing device having toothed rings of which only 10 percent of the teeth establish a permanent contact between cylindrical walls 1 and 3 and serve to maintain the spacing device in position, nine out of 10 teeth being set back from the wall, from which they are separated by a very slight interval of the order of several tenths to about a mm.

The permanent support surface, source of thermal leaks, thus becomes 1] l 000 of the surface of cylindrical wall 1.

At the moment of short-circuit, and to the extent that the permanent supports do not suffice to sustain the stress, a very slight deformation of cylinder 3, deforming in a direction toward implosion, i.e., toward core 2, cause the supplementary spacers to enter into supporting contact with cylinder 1 and thereby limit any excessive deformation that could affect airtightness of the joints of the assembly.

The interval separating the support props set back from cylindrical wall 1 from this wall is chosen so that the allowable slight deformation will in no way harm airtightness.

Each ring 12 may, for example, have 25 teeth, each of which may exhibit a support surface of 1 cm. In all, for a cylindrical wall height of 1.2 m, a dozen uniformly spaced rings could be arranged, giving a total support surface of 300 cm.

These rings are, as may be seen in FIG. 4, set in series along assembly rods 14, being made up of a unidirectionally layered material with a glass/epoxy resin base and separated by braces 15 formed of glass/epoxy resin cylinders. Assembly rodsand brace cylinders are adhered together and to rings 12.

Mounting is best effected so that assembly rods 14 radially face the cut-out portions 16 (FIG. 2) of rings 12, and so that all of the teeth of rings 12 are aligned along a generatrix line of cylinder 1.

Out of the assembly of 300 support points formed by the 25 teeth of the 12 rings, 30 are permanent support points and 270 are occasional support points, the teeth corresponding to the occasional support points being set back from one-tenth mm to 1 mm with'respect to cylindrical wall 1.

In order to ensure optimal spacing, as may be seen in FIG. 5, the permanent support point teeth are located on the topmost and bottommost of rings 12, as well as on one or more median rings (not shown) for long units, whereas the set back teeth are distributed among the intermediate rings 12.

It is advantageous for the solid part of the ring to possess sufiicient width, equal to or greater than 25 mm. In effect, in these conditions, cylinder 3 and the solid annular portion of rings 12 contribute to the mechanical rigidity of the assembly. The stress on the teeth is then decreased and, although the resistance to crushing of the material above referred to is only 2,000 kg/cm', it is possible to make 300 teeth sustain an overall stress of 1,000 tons when they would normally not be capable of sustaining more than 600 tons.

Moreover, this system of spacing between the wall of cylinder 3 and the wall of cylinder 1 exhibits a resistance to crushing which is regularly distributed along the entire circumference and sustains the electrodynamic short circuit stresses of 1,000 tons exerted on the surface of cylinder 3 even if the application of these stresses occurs in a asymmetrical fashion; measured variations of mechanical resistance do not exceed 3 percent according to whether the stress is appliettli1 directly to the teeth or between two consecutive tee To decrease heat loss, and increase mechanical strength, the outer, i.e., support surface of teeth 13 may be metal plated. 5

It is obviously possible within the scope of the present invention to decrese the number of support points in reducing the number of teeth, just as long as the support surface of each tooth is proportioned to the proper share of the total stress which it will then have to sustain.

The assembly of the device of the present invention to a transformer core 2, not shown in detail, is conventional, and a transformer in which the invention can be used is shown in US. Pat. No. 3,396,355.

I claim: 1. Cryogenic electrical power apparatus having double wall construction in which the walls are subject to deformation forces on the apparatus under overload conditions thereof comprising inner wall means (3, 6, 7, 8) forming an inner enclosure (4) adapted to contain cryogenic fluid;

outer wall means (1, 9, 10, 11) forming an outer enclosure surrounding said inner enclosure, the space (5) between said enclosures being evacuated to prevent heat transmission between said wall means and to provide for thermal insulation between said enclosures and thermal insulation of the cryogenic fluid within the inner enclosure;

plate-like spacer means located in the space (5) between said wall means fonning said enclosure to maintain said wall means in mutually spaced relationship, said spacer means being formed, towards at least one of said wall means, with a toothed surface, the teeth forming said surface being of two types:

type a: support and bearing teeth, in permanent contact with the facing wall means; and

type b: shorter support and bearing teeth, slightly spaced from the facing wall means, the spacing being selected to permit contact between the shorter support and bearing teeth and the adjacent, facing wall means upon occasional deformation due to overload conditions of the apparatus tending to move said facing wall means towards each other and thereby provide additional bearing and support surface area during said overload, but, absent such deformation, being out of contact with said facing wall means and thus avoid 50 contact with the wall means only occasionally, is metal plated.

4. Construction according to claim 1, wherein the spacing of the shortened type b teeth from the facing wall means is between about 0.1 mm to 1 mm.

5. Construction according to claim 1, wherein a plurality of spacer means are provided, the surface of the type a teeth forming a permanent support surface in ena ement with the facin wall means and bein of r n ch less area than the su rface of the type b teeth facing the adjacent wall means.

6 Construction according to claim 1, wherein the area of the type a teeth forming a permanent support surface is of the order of one-tenth of the area of the type b teeth forming an occasional support surface.

7. Construction according to claim 1, wherein the area of the type a teeth facing the adjacent wall means and forming a permanent support surface is of the order of one-thousandth of the surface of the corresponding facing wall means.

8. Construction according to claim 1, wherein the spacers are formed of a layered insulating material comprising fabric or glass fiber plies bonded with a synthetic resin.

9. Construction according to claim 8, wherein the synthetic resin is an epoxy resin.

10. Construction according to claim 8, wherein the layers of fiber are perpendicular to the wall means of the enclosure.

11. Construction according to claim 1, wherein the wall means are cylindrical, said spacer means being located therebetween and form rings arranged with a space between them and distributed along the entire axial length between the wall means, said rings presenting said teeth in arrays along at least one of their exterior or interior circumferences, the teeth of some of the rings being in permanent contact with the facing wall; and at least the major portion of the teeth of the other rings being of the type b teeth and spaced from the wall means.

12. Construction according to claim 11, wherein the solid portion of the rings has a width of at least 25 mm. 

1. Cryogenic electrical power apparatus having double wall construction in which the walls are subject to deformation forces on the apparatus under overload conditions thereof comprising inner wall means (3, 6, 7, 8) forming an inner enclosure (4) adapted to contain cryogenic fluid; outer wall means (1, 9, 10, 11) forming an outer enclosure surrounding said inner enclosure, the space (5) between said enclosures being evacuated to prevent heat transmission between said wall means and to provide for thermal insulation between said enclosures and thermal insulation of the cryogenic fluid within the inner enclosure; plate-like spacer means located in the space (5) between said wall means forming said enclosure to maintain said wall means in mutually spaced relationship, said spacer means being formed, towards at least one of said wall meanS, with a toothed surface, the teeth forming said surface being of two types: type a: support and bearing teeth, in permanent contact with the facing wall means; and type b: shorter support and bearing teeth, slightly spaced from the facing wall means, the spacing being selected to permit contact between the shorter support and bearing teeth and the adjacent, facing wall means upon occasional deformation due to overload conditions of the apparatus tending to move said facing wall means towards each other and thereby provide additional bearing and support surface area during said overload, but, absent such deformation, being out of contact with said facing wall means and thus avoid heat transmission by conduction between the shorter teeth and the facing wall means.
 2. Construction according to claim 1, wherein the teeth of the plate-like spacer means have a trapezoidal shape.
 3. Construction according to claim 1, wherein the surface of the shortened type b teeth and coming into contact with the wall means only occasionally, is metal plated.
 4. Construction according to claim 1, wherein the spacing of the shortened type b teeth from the facing wall means is between about 0.1 mm to 1 mm.
 5. Construction according to claim 1, wherein a plurality of spacer means are provided, the surface of the type a teeth forming a permanent support surface in engagement with the facing wall means and being of much less area than the surface of the type b teeth facing the adjacent wall means.
 6. Construction according to claim 1, wherein the area of the type a teeth forming a permanent support surface is of the order of one-tenth of the area of the type b teeth forming an occasional support surface.
 7. Construction according to claim 1, wherein the area of the type a teeth facing the adjacent wall means and forming a permanent support surface is of the order of one-thousandth of the surface of the corresponding facing wall means.
 8. Construction according to claim 1, wherein the spacers are formed of a layered insulating material comprising fabric or glass fiber plies bonded with a synthetic resin.
 9. Construction according to claim 8, wherein the synthetic resin is an epoxy resin.
 10. Construction according to claim 8, wherein the layers of fiber are perpendicular to the wall means of the enclosure.
 11. Construction according to claim 1, wherein the wall means are cylindrical, said spacer means being located therebetween and form rings arranged with a space between them and distributed along the entire axial length between the wall means, said rings presenting said teeth in arrays along at least one of their exterior or interior circumferences, the teeth of some of the rings being in permanent contact with the facing wall; and at least the major portion of the teeth of the other rings being of the type b teeth and spaced from the wall means.
 12. Construction according to claim 11, wherein the solid portion of the rings has a width of at least 25 mm. 